At the heart of London lies a haven of serene beauty. When fretful crowds are jostling and craning to see the latest underground blockbuster, you can glide up the staircase of the National Gallery’s Sainsbury Wing and find a moment of peace among splendour. This is more than just the finest collection of early Renaissance art to be found outside Italy. It is a salve to the soul.

In the summer of 2015 a new treasure was added to this extraordinary collection. Thanks to a donation from the philanthropist Ronald S Lauder, the gallery was able to acquire (with the proviso that it would be loaned to Lauder during his lifetime, but shown at regular intervals at the National Gallery) one of the loveliest panel…